B.2 Greenhouse effect
Practice exam-style IB Physics questions for Greenhouse effect, aligned with the syllabus and grouped by topic.
Question 1
A surface scatters 90 W of incident solar power when 300 W is incident on it. What is the albedo of the surface?
A.
0.23
B.
3.3
C.
0.70
D.
0.30
Question 2
What is meant by the emissivity of a surface?
A.
The fraction of incident solar radiation reflected by the surface
B.
The wavelength at which the surface emits maximum intensity
C.
The ratio of radiated power per unit area to σT⁴ for the same temperature
D.
The total power incident per unit area perpendicular to the radiation
Question 3
The solar constant at a planet is 1600 W m⁻². The planet has negligible albedo. What is the mean incoming solar intensity over the whole planetary surface?
A.
400 W m⁻²
B.
800 W m⁻²
C.
6400 W m⁻²
D.
1600 W m⁻²
Question 4
Which gas is a main greenhouse gas in Earth's atmosphere?
A.
Nitrogen, N₂
B.
Carbon dioxide, CO₂
C.
Oxygen, O₂
D.
Argon, Ar
Question 5
What does the solar constant represent?
A.
The mean temperature of the solar surface in kelvin
B.
The average solar power absorbed by one square metre of Earth's surface after reflection
C.
The intensity of solar radiation at Earth's mean orbit on a plane perpendicular to the rays
D.
The total power radiated by the Sun
Question 6
A region of Earth's surface receives an incident solar intensity of 520 W m⁻². Its albedo is 0.35.
Calculate the reflected intensity.
[1]
Calculate the absorbed intensity.
[1]
State why albedo has no unit.
[1]
Question 7
Outline what is meant by dynamic equilibrium for the Earth–atmosphere energy system. [2]
Question 8
A planet has albedo 0.25 and solar constant 1200 W m⁻². What is the mean absorbed solar intensity?
A.
900 W m⁻²
B.
225 W m⁻²
C.
1200 W m⁻²
D.
300 W m⁻²
Question 9
What happens after a greenhouse-gas molecule absorbs an infrared photon emitted by Earth's surface?
A.
It permanently stores the photon energy as chemical energy.
B.
It may transfer energy by collisions or re-emit infrared radiation in any direction.
C.
It must immediately emit a visible photon vertically upwards.
D.
It reflects the photon without changing molecular energy levels.
Question 10
A grey surface at 300 K has emissivity 0.80. What is the power radiated per unit area? Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
A.
37 W m⁻²
B.
367 W m⁻²
C.
459 W m⁻²
D.
573 W m⁻²
Question 11
A molecular vibration absorbs infrared radiation strongly only if the vibration
A.
has a natural frequency in the ultraviolet region.
B.
changes the electric dipole of the molecule.
C.
has the same amplitude for every greenhouse gas.
D.
occurs only in monatomic gases.
Question 12
What is the enhanced greenhouse effect?
A.
The complete trapping of all infrared radiation by nitrogen and oxygen
B.
The reflection of more visible sunlight by clouds and ice
C.
The daily variation in Earth's albedo due to cloud movement
D.
The human-caused augmentation of greenhouse warming due to increased greenhouse-gas concentrations
Question 13
The solar constant is S for a spherical planet of radius R.
State the projected area that intercepts the solar radiation.
[1]
Show that the mean incoming intensity over the whole surface before reflection is S/4.
[1]
Question 14
State two main greenhouse gases other than carbon dioxide.
[1]
State one human activity that increases atmospheric carbon dioxide concentration.
[1]
Question 15
Explain why greenhouse gases warm Earth's surface even though they do not absorb all incoming visible sunlight. [3]
Question 16
A flat panel of area 2.0 m² at 295 K has emissivity 0.75.
Calculate the power radiated by the panel.
[1]
State one reason why the panel is described as a grey body rather than a black body. [1]
Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
[1]
Question 17
The graph shows the monthly mean albedo of two regions, X and Y, during one year.
Identify the region with the greater seasonal variation in albedo.
[1]
Estimate the month in which region X has its maximum albedo.
[1]
Suggest a physical cause of the seasonal change in albedo for a polar region.
[1]
Explain how a decrease in polar albedo can affect absorbed solar radiation.
[1]
Question 18
The graph shows the transmittance of a sample of atmosphere for infrared radiation over a range of wavelengths. Absorption bands of selected gases are labelled.
State the wavelength range where the atmosphere has the greatest transmittance.
[1]
Identify one gas responsible for a low-transmittance band.
[1]
Explain why low transmittance at an infrared wavelength can contribute to the greenhouse effect.
[1]
Question 19
The table gives changes in atmospheric concentrations of four greenhouse gases over a period of years.
| Gas | Initial conc. / ppm | Final conc. / ppm |
|---|---|---|
| CH₄ | 0.72 | 1.90 |
| H₂O | 10000 | 10600 |
| CO₂ | 280 | 420 |
| N₂O | 0.270 | 0.334 |
Identify the gas with the largest percentage increase.
[1]
State one human source of methane.
[1]
Explain why water vapour is often treated as a feedback rather than the main direct human forcing.
[1]
Question 20
In a simple model, the fraction k of surface infrared radiation returned to the surface by the atmosphere increases. Solar input and albedo remain constant. What happens to the equilibrium surface temperature?
A.
It increases so that the escaping infrared radiation again balances absorbed solar radiation.
B.
It decreases because less infrared radiation is emitted by the surface.
C.
It becomes independent of emissivity because greenhouse gases absorb visible radiation.
D.
It remains constant because incoming solar radiation is unchanged.
Question 21
The luminosity of a star is 3.0 × 10²⁶ W. A planet orbits at 1.5 × 10¹¹ m. What is the stellar constant at the planet?
A.
4.2 × 10³ W m⁻²
B.
530 W m⁻²
C.
2120 W m⁻²
D.
1060 W m⁻²
Question 22
Sea ice melts and is replaced by open ocean. What is the direct effect on absorbed solar radiation in that region?
A.
It decreases because ocean has a higher albedo than sea ice.
B.
It is unchanged because albedo affects only infrared radiation.
C.
It increases because the albedo decreases.
D.
It becomes zero because all radiation is transmitted into the ocean.
Question 23
A moon with emissivity 1.0 and albedo 0.40 receives a solar constant of 900 W m⁻². What is the equilibrium temperature, assuming it radiates directly to space? Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
A.
221 K
B.
316 K
C.
399 K
D.
278 K
Question 24
Why is the resonance model of greenhouse absorption limited?
A.
It ignores that molecular energies are quantized and that only some vibrations are infrared-active.
B.
It applies only to visible light absorbed by the ground.
C.
It predicts that no molecule can absorb infrared radiation.
D.
It requires every atmospheric molecule to have the same natural frequency.
Question 25
A surface at 310 K radiates 420 W m⁻². What is its emissivity? Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
A.
4.8
B.
0.80
C.
1.25
D.
0.95
Question 26
A rocky body has albedo 0.20, emissivity 0.90 and receives a solar constant of 1000 W m⁻². It radiates directly to space.
Calculate the mean absorbed solar intensity.
[1]
Determine the equilibrium temperature. Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
[1]
Question 27
A climate model predicts that a warming Arctic will have a lower average surface albedo.
Suggest a physical reason for this prediction.
[1]
Explain how this can act as a positive feedback.
[1]
Question 28
A satellite radiates to cold space from a surface of area 1.8 m² and emissivity 0.62. Its surface temperature is 285 K and the surroundings may be treated as 3 K.
Write down the expression for the net radiative power loss.
[1]
Calculate the net radiative power loss.
[1]
State why the 3 K surroundings make a negligible difference here.
[1]
Question 29
In a simple greenhouse model,
(1 − k)σT_s⁴ = (1 − a)S/4.
For a planet, a = 0.30, S = 1360 W m⁻² and k = 0.40.
Calculate the absorbed solar intensity.
[1]
Calculate T_s. [2]
Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
[1]
Question 30
Distinguish between albedo and emissivity. [3]
Question 31
The atmosphere has high transmittance in some infrared wavelength ranges and low transmittance in others.
State what is meant by transmittance.
[1]
Explain why the atmospheric transmittance depends on wavelength.
[1]
Question 32
A country replaces coal-fired power stations with wind and solar generation.
State the main greenhouse gas whose direct operational emission is reduced.
[1]
Explain how this change can affect the energy balance of the atmosphere.
[1]
Question 33
A table gives the solar constant and albedo for four small airless moons.
| Moon | Solar constant / W m⁻² | Albedo |
|---|---|---|
| A | 1000 | 0.28 |
| B | 760 | 0.10 |
| C | 900 | 0.15 |
| D | 1200 | 0.45 |
Identify the moon with the largest mean absorbed solar intensity.
[1]
Calculate the mean absorbed solar intensity for moon A.
[1]
The emissivity of moon A is 1.0. Determine its equilibrium temperature. [2]
Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
[1]
Question 34
A simplified energy-flow diagram for a planet shows mean incoming solar intensity, reflected solar intensity and outgoing infrared intensity at the top of the atmosphere.
Determine whether the planet is warming, cooling or in radiative balance.
[1]
Calculate the net radiative imbalance.
[1]
State the conservation principle used in part (a).
[1]
Suggest one reason why a short-term imbalance may not imply a permanent change in climate.
[1]
Question 35
Carbon dioxide has several vibrational modes. The symmetric stretching mode is weakly infrared-active, while bending modes are strongly infrared-active.
State the resonance condition for efficient absorption of infrared radiation.
[1]
Explain why not every vibrational mode produces strong infrared absorption.
[1]
State one limitation of a purely classical resonance explanation.
[1]
Question 36
A star has luminosity 6.0 × 10²⁶ W. A planet orbits the star at 2.0 × 10¹¹ m with albedo 0.25 and emissivity 1.0.
Calculate the stellar constant at the planet.
[1]
Calculate the mean absorbed intensity.
[1]
Determine the equilibrium temperature of the planet. [2]
Use σ = 5.67 × 10⁻⁸ W m⁻² K⁻⁴.
[1]
Question 37
A simplified model treats the atmosphere as returning a fixed fraction k of all infrared radiation emitted by Earth's surface.
State one useful feature of this model.
[1]
State two limitations of this model.
[1]
Suggest why such simplified models are still used.
[1]
Question 38
The graph shows modelled equilibrium surface temperature as a function of the greenhouse parameter k for a planet with constant solar constant and albedo.
Describe the trend shown by the graph.
[1]
Use the graph to estimate the temperature change when k increases between two marked values.
[1]
Explain, using (1 − k)σT_s⁴ = constant, why the trend is non-linear.
[1]
State one limitation of representing the atmosphere with a single parameter k.
[1]
Question 39
The graph shows radiated power per unit area against T⁴ for three surfaces of the same material treatment but different colours in visible light.
State how emissivity can be determined from the graph.
[1]
Identify the surface with the greatest infrared emissivity.
[1]
Calculate the emissivity of surface B using the gradient of its line.
[1]
Explain why visible colour alone is not sufficient to determine infrared emissivity.
[1]
Question 40
The diagram shows absorption intensity for three vibrational modes of a greenhouse-gas molecule, together with the change in electric dipole during each mode.
| Vibrational mode | Dipole change / a.u. | Absorption / a.u. |
|---|---|---|
| Symmetric stretch | 0.05 | 0.02 |
| Bending mode | 0.55 | 0.48 |
| Asymmetric stretch | 1.00 | 0.96 |
Identify the mode with the strongest infrared absorption.
[1]
State the relationship between dipole change and absorption shown by the data.
[1]
Explain why nitrogen and oxygen are not main greenhouse gases using this idea.
[1]
Question 41
A Sankey-style diagram shows annual energy flows for a simplified surface–atmosphere system: absorbed solar radiation, surface infrared emission, atmospheric infrared absorption, downward infrared re-emission and energy transferred by convection/evaporation.
Determine the net energy gain or loss of the surface.
[1]
Identify the largest energy transfer from the surface to the atmosphere.
[1]
Explain why the diagram is consistent with the greenhouse effect.
[1]
Suggest one improvement to make the model more realistic.
[1]
Question 42
A planet has no atmosphere. Its albedo is a and the solar constant at its orbit is S.
Show that the mean absorbed solar intensity is (1 − a)S/4.
[1]
Explain how this expression is used to estimate the planet's equilibrium temperature, including the role of emissivity.
[1]
Question 43
Greenhouse gases interact differently with incoming solar radiation and outgoing radiation from Earth's surface.
Describe the change in wavelength of radiation involved in the greenhouse effect.
[1]
Discuss how molecular energy levels and re-emission lead to warming of the surface.
[1]
Question 44
Earth's average albedo is often quoted as about 0.30.
Outline two causes of variation in Earth's albedo.
[1]
Evaluate the importance of albedo feedback in climate warming.
[1]
Question 45
The table gives the distance from a star and the measured stellar constant for three planets. The star's luminosity is constant.
| Planet | Orbital distance / m | Measured stellar constant / W m⁻² |
|---|---|---|
| P | 1.50 × 10¹¹ | 1.40 × 10³ |
| Q | 2.00 × 10¹¹ | 7.9 × 10² |
| R | 3.00 × 10¹¹ | — |
State the inverse-square relationship being tested.
[1]
Use the data for planet P to calculate the luminosity of the star.
[1]
Predict the stellar constant at the orbit of planet R using the luminosity found in (b).
[1]
Suggest one reason why a measured value may differ slightly from the prediction.
[1]
Question 46
Human activities can enhance the natural greenhouse effect.
State two human activities that increase greenhouse-gas concentrations.
[1]
Discuss, using energy balance, how these activities can change Earth's mean surface temperature.
[1]
Question 47
A simple one-parameter atmosphere model is described by
(1 − k)σT_s⁴ = (1 − a)S/4,
where k is the fraction of surface infrared radiation returned to the surface.
Derive an expression for T_s in terms of k, a and S.
[1]
Evaluate the usefulness and limitations of this model for explaining the enhanced greenhouse effect.
[1]
Question 48
The greenhouse effect may be explained using a resonance model and using molecular energy levels.
Outline the resonance model for infrared absorption by a greenhouse gas.
[1]
Compare and contrast the resonance model with the molecular energy-level explanation, including limitations of the resonance model.
[1]
Question 49
Different electricity-generation methods have different effects on the atmospheric energy balance.
Outline two ways in which fossil-fuel electricity generation can increase greenhouse-gas concentrations.
[1]
Discuss how replacing fossil-fuel generation with low-carbon generation affects the greenhouse effect, including one limitation of the comparison.
[1]
Question 50
A proposed geoengineering method would increase Earth's average albedo by adding reflective particles to the upper atmosphere, while greenhouse-gas concentrations continue to rise.
Explain, using the absorbed solar intensity expression, the direct effect of increasing albedo.
[1]
Evaluate whether increasing albedo alone would fully cancel the physical effects of rising greenhouse-gas concentrations.
[1]
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